This invention relates to multilayer film structures. More particularly it relates to self unified, heat sealable multilayer film structures comprising a layer of polyester chemically interfacially bonded to a layer of a polyolefinic material containing a fatty acid amide.
Self-unified, heat sealable films have been previously described. Thus, see U.S. Pat. Nos. 3,188,265 and 3,188,266. These patents describe films which comprise a polyester layer having a polyethylene layer chemically interfacially bonded thereto. The films are prepared by laminating the two layers together and then irradiating the laminate with ultraviolet radiation to provide a bond which is mechanically inseparable. The resulting films, commercially available as SCOTCHPAK.RTM. films from Minnesota Mining and Manufacturing Company, have been found to be very useful especially as heat sealable packaging films for a wide variety of materials such as frozen foods, cooking oils, lubricants adhesives, tobacco, detergents and hardware.
However, the use of additives such as slip agents, has been avoided in the past in these films because it was felt that they deleteriously affected the chemical interfacial bond between the polyester and the polyethylene. The absence of slip agents in such films, however, has proven troublesome when the films are processed and converted into a package.
Slip agents are known to act as plasticizers and lubricants which reduce the resistance of films to being pulled across machine parts. This resistance, known as film surface drag, is very detrimental to high speed film processing. Consequently, the incorporation of slip agents into self unified, heat sealable films would be highly beneficial if it could be accomplished without adversely affecting the chemical interfacial bond between the polyester and the polyethylene.
It has now been discovered that certain slip agents may be incorporated into the polyethylene layer of self unified, heat sealable films in limited amounts without adversely affecting the interfacial bond even though the slip agents have a plasticizing effect upon the polyethylene layer. Still further, the addition of the slip agent does not materially affect the strength of any heat sealed bond subsequently formed.